Imidazole derivatives of formula I wherein n is 0 or 1, R1 is hydrogen or C1-C4-alkyl, R2 is hydrogen or R2 and R3 together form a double bond, R3 is hydrogen or C1-C4-alkyl or R2 and R3 together form a double bond, R4 is hydrogen, C1-C4-alkyl, hydroxy or C1-C4-alkoxy, R5 is hydrogen or C1-C4-alkyl or R4 and R5 together with the carbon atom to which they are attached form a carbonyl group, R6, R7 and R8 are each the same or different and are independently hydrogen, C1-C4-alkyl or C2-C4-alkenyl, C3-C7-cycloalkyl, hydroxy, C1-C4-alkoxy, C1-C4-hydroxyalkyl, thiol, C1-4-alkylthio, C1-4-alkylthiol, halogen, trifluoromethyl, nitro or optionally substituted amino, X is —CHR9—(CHR10)m—, m is 0 or 1, and R9 and R10 are each the same or different and are independently hydrogen or C1-C4-alkyl; or a pharmaceutically acceptable ester or salt thereof, their preparation, use and pharmaceutical compositions comprising them are described. The compounds have affinity for alpha2 receptors and are useful e.g. in the treatment of hypertension, glaucoma, chronic or acute pain, migraine, diarrhea, common cold, ischemia, addiction to chemical substances, anxiety, especially preoperative anxiety and different neurological, musculoskeletal, psychiatric and cognition disorders or as adjuncts to anesthesia.